In a world where energy efficiency has become a crucial industrial, economic and even household issue, it is important to take energy conversion efficiency into consideration in power and energy conversion systems and in engines in particular. The current state of the art for engines is dominated by internal combustion engines based upon open-loop Otto cycle, Diesel cycle, or Brayton thermodynamic power cycles. Engines based upon these cycles are sufficiently efficient for many applications, being typically represented by automobiles, heavy trucks and aircraft turbines respectively.
Otto Cycle and Diesel Cycle engines are used primarily for application in internal combustion engines for automobile and other low cost consumer applications. These types of engines are adequately efficient, lightweight, and relatively inexpensive to manufacture for wide use, with relatively low consequent unit costs resulting from the economy of scale.
Internal combustion engines typically employ air as a working fluid. Combustion heat is created by injecting and burning fuel with the air as a working fluid at suitable points and times in the thermodynamic cycle of the engine. This enables the working fluid to be expanded and to perform work. For a number of reasons these engines produce much less power than their theoretical limits. Much focus has therefore been on improving the designs and efficiencies for these types of engines as a means to convert power.
Problems associated with conventional internal combustion engines include: typical efficiencies of only approximately 20% to 40%; the need for specific fuel types for each type of engine; and significant emissions of green house gas and other air pollutants. Several of the reasons for the limitations in efficiency are founded in the fact that the compression, combustion and expansion all happen in the same volume. Given the vagaries of timing, fuel supply, ignition, and inherently incomplete expansion of the working fluid in these engines, the thermodynamic cycles of these systems are notoriously difficult to optimize within one volume.
The ideal thermodynamic model for an engine is the Carnot cycle, but its efficiencies are not achievable in practical engine systems. Thermodynamic engine cycles based on isothermal compression or expansion hold most promise of high efficiency. Unfortunately, suitable isothermal compression or expansion is difficult to achieve under practical conditions without resorting to complex and bulky heat exchangers, and/or injecting substantial volumes of direct contact heat exchange fluids into the process flow, which also adds complexity and can increase losses. True isothermal compression or expansion remains in the domain of theory, along with the Carnot cycle itself.
The present technology is addressed to the above challenges in respect of engines as they pertain to the field of power generation, storage and use.